This project is mainly GCD and validating the error from user input. I got the GCD working correctly, but not the errors. Here's guidelines to validate the errors.

-Provide a function to get a nonzero positive integer from the keyboard and return it to the caller.

int get_input()

-If input is not valid, the function should output an error message and repeat the input operation.
-Be sure your input function works correctly with invalid inputs. Even inputs that are not integers:

123.456 (Should return 123)
abc (Should output error message and repeat input.)

Now here's the problem. Everything compiles with no problems. When I input zero for X, it moves on and ask for Y. Now, it's not suppose to do that. It's suppose to output an error message and asking me for a different input. Also, a similar problem with decimal numbers like 123.123. It just automatically ends the program with decimal numbers. Here is a sample output:

Enter integer X: 0
Please enter an integer greater than 0
123.456
Enter integer Y: Please enter an integer greater than 0
abc
Please enter an integer greater than 0
44
The GCD of 123 and 44 is 1

Here's what I have.

#include <stdio.h>

int gcd(int x, int y);

int gcd(int x, int y) 
{ 
   if (y == 0) 
   return x;
   
   else 
   return gcd(y, x % y);
}
	
int get_input()
{
	int x, y;
	
	while(1)
	{
		if(scanf("%d", &x) != EOF)
		{
			if (x > 0)
			return x;
		}
		
		if(scanf("%d", &x) != EOF)
		{
			if (y > 0)
			return y;
		}
		
		else
		{
		printf("Input error\n");
		printf("Please enter an integer greater than 0\n");
		while(getchar() != '\n'); // Clear the input buffer
		}
	}
}

int main()
{
	int x, y, common;
	
	printf("This program computes the greatest common divisor\n");
	printf("of positive integers X and Y, entered by the user.\n");
	printf("Inputs must be integers greater than zero.\n\n");
	
	printf("Enter integer X: ");
	x = get_input();
	printf("Enter integer Y: ");
	y = get_input();
	
	common = gcd(x,y);
	
	printf("The GCD of %d and %d is %d\n", x, y, common);
	return 0;
}

Any help getting me in the right direction is greatly appreciated. Thanks!

>When I input zero for X, it moves on and ask for Y. Now, it's not suppose to do that. It's suppose to output an error message and asking me for a different input.

The get_input () has a logic flaw then.
It asks for X and then for Y, when it should ask only for either X or Y.

Edit:

Continuous loop:
     Display question
         if input entered
             is x more than 0
                 return x
             x is not more than 0
                 Display error and it will loop again

Ok, I got that, but I'm a bit confused in understanding why it works like that. Why is only one of the variables, x or y, needed for it to work?

Also, how would I make it read decimal numbers, round it, and accept it? For example, 123.123 is entered, so 123 suppose to be read. I'm also trying to find out how to do this.

>but I'm a bit confused in understanding why it works like that. Why is only one of the variables, x or y, needed for it to work?

That's the way you designed. Functions can only return one value. And you are calling that function once for X and another time for Y in main.

>Also, how would I make it read decimal numbers, round it, and accept it? For example, 123.123 is entered, so 123 suppose to be read. I'm also trying to find out how to do this.

Read on.

Ok, I understand how to the rounding because I remember I did a past project on it before, but the program isn't even accepting it. When I input 123.123, it automatically ends the program when it should just continue on and ask for y.

Without code, I can not guess what kind of modification you had done.
For rounding up you can take a look at the ceil() function in the math.h as well.

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